Devices for sensing the presence of one or more persons in a room are used extensively for the purpose of actuating security alarms and can also serve a variety of other purposes. Energy savings can be realized by using such devices to turn on lights, heating, air conditioning or other equipment only when it is actually needed and to turn such facilities off when a room is unoccupied.
One type of occupancy sensor responds to the infrared energy which is radiated by the human body. Such sensors include a pyroelectric component of the type which exhibits an electrical voltage or a change of electrical resistance in response to infrared radiation. Circuits in the sensor detect this change and respond by transmitting an actuating signal to one or more electrically controlled devices that are to be turned on when the room is occupied.
Such sensors may also include means for intercepting infrared that arrives from different directions and for concentrating the intercepted infrared at the location of the pyroelectric component. This broadens the range of the sensor. Prior sensors typically use reflectors for this purpose. This has an adverse effect on sensitivity as significant losses of infrared energy occur during the process of reflection.
Intercepted infrared can also be focused towards the location of the pyroelectric component by lenses which are inherently more efficient than reflectors. Prior lenses for this purpose have an undesirably narrow field of view and this makes it necessary to provide a complex and costly assembly of such lenses if the sensor must detect a person at any location within a sizable room.
Sensors of the above described kind have a detection pattern which is the outline of region within which the sensor will detect infrared. The ideal pattern varies from room to room. For example, a detection pattern that approximates a square is appropriate for rooms which have a similar configuration while a long narrow pattern is more appropriate for a hallway. Tailoring of the detection pattern to accommodate to the requirements of different rooms is an undesirably complicated process in the prior occupancy sensors as it requires restructuring of a number of different components. Testing of the prior sensors at the time of installation, to assure that it responds to the presence of a person at different locations in a room, is an undesirably complicated and time consuming process.
The present invention is directed to overcoming one or more of the problems discussed above.